Student Thinking Regarding Entropy and the Second Law of Thermodynamics *

1. Student Thinking Regarding Entropy and the Second Law of Thermodynamics * Warren Christensen Iowa State University PERG David Meltzer University of Washington *Supported in part by NSF grants #DUE-9981140 and #PHY-0406724.

2. Context of Investigation • Part of a broad study of student understanding of thermodynamics in a second semester calculus-based physics course at Iowa State University • In collaboration with John Thompson at the University of Maine and David Meltzer at the University of Washington in upper-level thermal physics courses

3. Pre-instruction Testing • Initial testing took place before all instruction on entropy and the second law of thermodynamics

4. Spontaneous Process Question For each of the following questions consider a system undergoing a naturally occurring (“spontaneous”) process. The system can exchange energy with its surroundings. • During this process, does the entropy of the system [Ssystem] increase, decrease, or remain the same, or is this not determinable with the given information? Explain your answer. • During this process, does the entropy of the surroundings [Ssurroundings] increase, decrease, or remain the same, or is this not determinable with the given information? Explain your answer. • During this process, does the entropy of the system plus the entropy of the surroundings [Ssystem + Ssurroundings] increase, decrease, or remain the same, or is this not determinable with the given information? Explain your answer.

5. Pre-instruction Data

6. 15% 29% 66% 19% 26%

7. Conservation Arguments • Conservation Argument #1 (29%) SSystem increases [decreases],SSurroundings decreases [increases], andSSystem + SSurroundings stays the same • Conservation Argument #2 (26%) SSystem not determinable, SSurroundings not determinable, and SSystem + SSurroundings stays the same

8. Pre- v. Post-Instruction Data Post-instruction testing showed small or negative gains

9. A Research-based Tutorial • We created a worksheet to address these ideas for use in the Spring 2006 course.

10. Insulated cube at TH Insulated cube at TL Conducting Rod Tutorial Design • Identify QH, QL, and discuss energy conservation • Calculate DSH, DSL, compare the magnitudes, and deduce entropy non-conservation

11. Pre/Post-instruction comparison

12. Conclusions • Before instruction students often apply ideas about energy conservation to entropy • Instruction with tutorials showed improved responses from students for some questions • This instruction is still in the early stages of testing and many questions are yet to be answered